1. Technical Field
The present invention relates to a method and apparatus for measuring a load applied to an elastic body on the basis of deformation of the elastic body caused by the applied load, and more particularly, to a method and apparatus for making an accurate load measurement by eliminating the influence of deformation of an elastic body comprised of a piezoelectric element on a measured object or a measured load.
2. Relevant Arts
Most load measuring devices are designed to make a load measurement based on a deformation amount of an elastic body observed when a load is applied thereto. A spring scale, a typical load measuring device, measures a load by utilizing the relation that the elongation of a spring is proportional to a load applied to the spring. A load cell which is another type of load measuring device is comprised of an elastic body, having a small elastic constant, and a strain gauge affixed to the elastic body. The load cell is adapted to measure a load applied to the elastic body by utilizing a change in resistance of the strain gauge caused by deformation of the strain gauge generated by the applied load.
In a load measurement based on deformation of an elastic body, the deformation of the elastic body generally has no substantial influence on a measured object or a measured load (a load to be measured). For example, in the case of measuring the weight of a measured object with use of a spring scale, a spring is elongated when the measured object is suspended from the spring, so that the distance between the measured object and the center of the earth decreases. In a strict sense, therefore, the gravitational force acting on the measured object increases. However, the elongation of the spring is extremely small and hardly affects the accuracy of load measurement.
In some cases, however, the deformation of the elastic body may affect a measured object or a measured load. For instance, in the case of using a load cell to measure a load applied to a wall from a body fixed to the wall when the body is heated, a load generated by the heat expansion of the body and applied to the wall causes the elastic body of the load cell to be deformed. The deformation of the elastic body changes a state of the measured object, resulting in an inaccurate measurement and a meaningless measurement.